Climate a Factor in Decline of Minnesota’s Moose Population

ST. PAUL, Minnesota, February 10, 2010 (ENS) – The moose population in northeastern Minnesota declined again this year, according to results of an aerial survey released Monday by the Minnesota Department of Natural Resources. The causes of this decline are not well understood, but some studies suggest a warming climate may be having an impact on Minnesota’s moose.

Survey results revealed lower moose numbers overall and the proportion of cows accompanied by calves continued a 13-year decline, dropping to a record low of 28 calves per 100 cows.

In addition to the decline in the calf to cow ratio, the bull to cow ratio also continued to decline with an estimated 83 bulls per 100 cows.

“These indices, along with results from research using radio-collared moose, all indicate that the population has been declining in recent years,” said Dr. Mark Lenarz, DNR forest wildlife group leader.

A study of radio-collared moose in northeastern Minnesota between 2002 and 2008 determined that non-hunting mortality was substantially higher than in moose populations outside of Minnesota. Lenarz indicated that, “combined with the reduced number of calves, the high mortality results in a population with a downward trend.”

Moose populations are estimated using an aerial survey of the northeast Minnesota moose range. Based on the survey, wildlife researchers estimate that there were 5,500 moose in northeastern Minnesota this year compared to the 7,600 estimated last year, reinforcing the picture of a declining moose population.

Aerial surveys have been conducted each year since 1960 in the northeast and are based on flying transects in 40 randomly selected plots spread across the Arrowhead region in the northeastern part of the state.

The Fond du Lac band of Lake Superior Chippewa and 1854 Treaty Authority contributed funding and provided personnel for the annual survey.

The causes of moose mortality are not well understood. Of 150 adult moose radio-collared since 2002 in Minnesota, 103 have subsequently died, most from unknown causes thought to be diseases or parasites.

Nine moose died as a result of highway vehicle accidents. Two were killed by trains. Only six deaths were clearly the result of wolf predation.

Analyses by Lenarz and other scientists have indicated a significant relationship between warmer temperatures and non-hunting mortality.

“Moose are superbly adapted to the cold but intolerant of heat,” said Lenarz, “and scientists believe that summer temperatures will likely determine the southern limit of this species.”

In August 2009, a Moose Advisory Committee convened by the Department of Natural Resources released its report finding that climate change is a threat to moose in the state.

Rolf Peterson, chair of the DNR Moose Advisory Committee, said the committee concluded that “while climate change is a long-term threat to the moose in Minnesota, moose will likely persist in the state for the foreseeable future.”

In northwestern Minnesota, an area of agricultural land interspersed with woodlots, the moose population has declined from 4,000 moose in the late 1980s to fewer than 100 today.

By contrast, the northeastern population inhabits wetland-rich forested habitat which provides thermal cover even in a warming environment.

Peterson, a professor at Michigan Technical University who studies wolf and moose in Isle Royale National Park in one of the world’s longest wildlife study, said committee members are concerned about high mortality among moose from health-related causes. Still, details are poorly understood.

“For example, the connections between parasites, disease and mortality exist but how they interrelate is not clear,” he said. “Managing white-tailed deer at a density of fewer than 10 per square mile would reduce the potential for parasite-mediated impacts on moose.”

Moose Advisory Committee members concluded unanimously that it is inappropriate at this time to designate the moose as either a threatened or endangered species under state law.

After considerable discussion, a narrow majority of committee members who voted supported state-listed status as a Species of Special Concern, which the committee said accurately reflects the animal’s vulnerable status but conveys no additional legal status or protections.

The committee recommended that moose hunting continue in northeastern Minnesota though key harvest and population data must be monitored as part of a strategy to identify when a closure would be appropriate.

The Moose Advisory Committee report will be used in the development of a research and management plan mandated by law. The plan should be ready for release this spring and will be open to the public for comment.